Organometallics 1987, 6, 335-343
335
second band (Rf0.24) yielded 0.065 g (17.2%) of 8, again as a of anhydrous dibutyl ether and 25 mL of anhydrous THF under moderately air-stable, orange crystalline solid. a dry nitrogen atmosphere. The mixture was refluxed for 24 h Complex 8 was also prepared directly from 7. In a typical during which time the colorless mixture became bright yellowexperiment, 0.100 g (0.181 mmol) of 7 and 0.398 g (1.81 mmol) orange. The solution was cooled to room temperature, opened of Cr(CO)6were placed in a 250-mL round-bottom flask, equipped to the air, and filtered and the solvent removed in vacuo. The as described above, and 100 mL of dibutyl ether and 10 mL of residue was chromatographed on a 2.5 X 60 cm silica gel column THF were added. The mixture was refluxed for 48 h, after which eluted with 20% methylene chloride-hexane. The colorless unit was cooled to room temperature and the solvent removed in reacted fluorene was eluted from the column first near the solvent vacuo to give an orange residue. This material was purifed as front. This was followed by a yellow band which yielded 2.84 g described to yield 0.065 g (52.1%) of 8. (18.8%) of (C13H10)Cr(C0),. This complex was isolated as a yellow-orange, moderately air-stable, crystalline solid which was stored in the dark under nitrogen prior to use. Acknowledgment. This work was supported by the Preparation of [2-((CO),CrPhCH2)-3-PhCHz-2,3-Army Research Office and by the donors of the Petroleum C2B4H4]Fe(CsHlo) (7) and [((CO)3CrPhCH~)zCzB4H4]Fe- Research Fund, administered by the American Chemical (CsHlo) (8). A 0.230-g (0.553-mmol)sample of 2 and 1.216 g (5.53 Society. We are grateful to Mr. Henry Boyter for obtaining mmol) of Cr(CO)6were placed in a 250-mL round-bottom flask the unit resolution mass spectra. equipped with a condenser and magnetic stirrer. Anhydrous Registry No. 1, 105472-14-8;2, 105472-15-9;3, 105472-16-0; dibutyl ether (100inL) and 10 mL of anhydrous THF were added, 4, 105472-17-1;5, 105500-99-0;6, 105472-18-2;7, 105472-19-3;8, and the mixture was refluxed under dry nitrogen for 48 h, during 105501-00-6;B,H,, 19624-22-7;FeCl,, 7758-94-3;P(OCH,),CCH,, which time the color gradually changed from colorless to orange. 1449-91-8; Cr(CO)6, 13007-92-6; trans-2,3-dibromo-2-butene, The reactor was cooled to room temperature and the solvent 21285-46-1;trans-2,3-dibromo-l,4-diphenyl-2-butene, 105456-31-3; removed in vacuo, the orange residue was dissolved in a minimum 1,4-diphenyl-2-butyne, 33598-23-1; 1,4-butynediol, 110-65-6; of methylene chloride,and the solution was chromatographed by 1,4-dichlorobutyne,821-10-3;cyclooctatetraene,629-20-9; [2.2]using 30% CH,Cl,-hexane as eluent. Two distinct orange bands paracyclophane, 1633-22-3; 9,10-dihydroanthracene, 613-31-0; were collected. The first band (Rf0.49) produced 0.132 g (43.1%) fluorene,86-73-7;(q3-fluorene)chromiumtricarbonyl, 33635-16-4. of 7 as an orange, crystalline, moderately air-stable solid. The
Organotransition-Metal Metallacarboranes. 10. .;rr-Complexation of nido-(PhCH2),C2B4H6 at the CpB3 and c6 Rings. Synthesis and Crystal Structures of nido-2,3-[ (co)3Cr(~6-C6H~)CH2]2-2,3-c2B4H6 and (PhCHp)&4B8H8, a Nonfluxional c4B8 Cluster' James T. Spencer,2aMohammad R. Pourian,2aRay J. Butcher,2bEkk Sinn,2aand Russell N. Grimes" 2a Departments of Chemistty, University of Virginia, Charlottesville, Virginia 2290 1, and Howard University, Washington, D.C. 20059 Received April 29, 1986
Reaction of the C,C'-dibenzyl-nido-carborane (PhCH2)&B4H6 (1)with NaH in T H F followed by FeC1, (2), which on treatment with O2 generates a tetrabenzyl forms a red complex, [(PhCH2)2C2B4H4]2FeH2 (3). Compound 3 is nonfluxional in solution, in contrast to previously tetracarbon cmborane, (PhCHz)4C4B~H~ studied R4C4B8Hsspecies where R = Me, Et, or n-Pr, and an X-ray diffraction study of 3 disclosed that the C4Bs cage is locked into an open-cage geometry as a consequence of severe intramolecular crowding (4), for which of the benzyl groups. Reaction of 2 with CpCo(CO), generates [(PhCH2)zCzB4H4]4FeCoCp a wedged structure is proposed. Treatment of 1 with Cr(COI6produces the mono- and dichromium complexes (5) and (CO)6Cr2(PhCH2)2C2B4H6 (6) as moderately air-sensitive solids which (C0)3Cr(PhCH2)2C2B4H6, were characterized from NMR, IR,and mass spectra and an X-ray crystallographic investigation of 6. Crystal data for 3: MI 507, space group P21f c , 2 = 4, a = 10.007 (2) A, b = 22.681 (6) A, c = 13.692 (2) A, fi = 110.18 (2)O, V = 2917 A3, R = 0.053 for 3813 reflections having F : > ~ U ( F , Crystal ) ~ . data for 6: MI 521, space grqup h a m , 2 = 4, a = 11.914 (2) A, b = 6.927 (1) A, c = 28.729 (6) A, V = 2371 A3, R = 0.044 for : > 30(FJ2. 1678 reflections having F T h e carborane derivative nido-2,3-dibenzyl-2,3-dicar- anion of 1, (PhCH2)2C2B4H5-,in combination with tranbahexaborane (PhCHJ2C2B4& (1) with its multifunctional sition-metal ions and arene ligands forms isolable, stable capability for ?r-coordination to transition metals has mixed-ligand sandwich complexes. Here we are concerned considerable potential for exploitation in organometallic with somewhat different aspects of dibenzylcarborane synthesis. As described elsewhere,' the conjugate base chemistry, namely, the formation of bis(dibenzy1carborany1)metal complexes and their oxidative fusion properties and the reactivity of the benzyl groups in 1 itself (1) Part 9 Spencer, J. T.; Grimes, R. N. Organometallics, second of toward metal complexation. Our primary purpose in this three papers in this issue. (2) (a) University of Virginia. (b) Howard University. study was to explore the steric and f or electronic influence 0276-7333f 87f 2306-0335$01.50 f 0 0 1987 American Chemical Society
336 Organometallics, Val. 6, No. 2, 1987
of the benzyl groups on the properties of the RzCzB4H6 nido-carborane cage. Heretofore, investigations of this carborane system, though e ~ t e n s i v e ?have ~ been limited mainly to derivatives in which R is relatively inactive5 (e.g., H or alkyl). The present work was considerably aided by the accessibility of 1 on a multigram scale as an air- (and water-!)stable liquid reagent.’
Results and Discussion Preparation of [ (PhCH2)2C2B4H4]2FeH2 and Conversion to (PhCH2)4C4B8H8. T h e synthesis of (R2C2B4H4)2MH, complexes (R = alkyl; M = Fe, x = 2; M = Co, x = 1) and the formation of R4C4B8H8carboranes via oxidative fusion of the RzC2B4H42-ligands is well established as a general reaction.‘j Metal-promoted fusion has been widely observed not only with carboranessi7but also with metallacarboranes,6 borane^,^^^ and metallaboranes.s In particular the conversion of two &C2B4H,2ligands to R4C4B8Hshas been extensively studied? and the C4B8cages are known to be fluxional, existing in solution as equilibrium mixtures of “open” and “closed” isomers.’0 When R = CH3, the quasi-icosahedral or “closed” form is predominant a t room temperature, while larger R groups (C2H5,n-C3H7)tend to favor the more open cage geometry. The availability of the dibenzylcarborane 1 presented us with an opportunity to examine the effects of very large R groups on both the fusion of R2C2B4H42units and the stereochemistry of the R4C4B8H8product(s). Indeed it was not certain, a priori, that fusion of (PhCH2)2C2B4H,2ligands would occur at all, given the large steric demands of the benzyl substituents. It was also conceivable that fusion, if it did take place, would occur in “backwards” fashion to give an edge-bonded (RzCzB4H4)z cluster with the R-C-C-R moieties a t opposite ends of the molecule. This latter mode of cage fusion has recently been observedg in the formation of B12H16from the BGHg-anion (a structural analogue of R2C2B4H,2-)and is attributed to the presence of several B-H-B bridges on the open faces of the hexaborane ligands (in this instance, less is known about the fusion process itself because the metallaborane intermediate has not been isolated). In this study, 1 was bridge-deprotonated with NaH and allowed to react with FeC12in T H F to give orange, moderately air-sensitive [ (PhCH2),C2B4H4I2FeH2 (2), characterized from its “B and ‘H NMR, infrared, and mass spectra (Tables I-IV). The spectral data on 2 closely
(3) (a) Spencer, J. T.; Grimes, R. N. Organometallics, first of three papers in this issue. (b) Swisher, R. G.; Sinn, E.; Grimes, R. N. Organometallics 1985,4,896and references therein. (c) Barton, L.; Rush, P. K. Znorg. Chem. 1986,25,91. (d) Briguglio, J. J.; Sneddon, L. G. Organometallics 1985,4,721.(e) Boyter, H. A., Jr.; Swisher, R. G.;Sinn, E.; Grimes, R. N. Inorg. Chem. 1985,24,3810.(f) Cowley, A. H.; Galow, P.; Hosmane, N. S.; Jutzi, P.; Norman, N. C. J. Chem. SOC.,Chem. Commun. 1984,1564. (4)For references to earlier work on nido-RzCzB,Hscarboranes, see: (a) Leach, J. B. Organomet. Chem. 1982,10,48. (b) Grimes, R. N. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E., Eds.; Pergamon Press: Oxford, England, 1982;Chapter 5.5. (c) Grimes, R. N. Coord. Chem. Reu. 1979,28,55. (5)The asymmetric derivatives 2-Ph(CH2),-2,3-CzB,H7!n = 2, 3)do have active phenylalkyl substituents and form complexes in which the phenyl and carborane rings are coordinated to the same metal ion: Swisher, R. G.; Sinn, E.; Grimes, R. N. Organometallics 1985,4, 890. (6) (a) Grimes, R. N. Acc. Chem. Res. 1983,16,22. (b) Adu. Inorg. Chem. Radiochem. 1983,26,55 and references therein. (7)Maynard, R. B.; Grimes, R. N. J. Am. Chem. SOC.1982,104,5983 and references therein. (8) Brewer, C. T.; Grimes, R. N. J. Am. Chem. SOC. 1985,107,3552. (9) Brewer, C.T., Swisher, R. G.; Sinn, E.; Grimes, R. N. J.Am. Chem. SOC. 1985,107,3558. (10)Venable, T. L.; Maynard, R. B.; Grimes, R. N. J. Am. Chem. SOC. 1984,106, 6187.
Spencer et al. Table I. 116.8-MHz llB FT NMR Datan compd 6(J~H HzIb , re1 areas (P~CHZ)ZCZB~HB (1) -0.43 (219), 1:2:1 -2.53 (149), -46.37 (180) [(PhCHz)2C2B4H412FeH2 (2) -1.46 (127), 1:2:1 -3.75 (1381, -47.18 (184) (PhCH2)&BaHa (3) -2.88: -12.86 (134) 3:l [(PhCH2)2C2B4Hl12FeC~(CSH6) -1.47: -2.31,c 1:1:3:1:1:1 (4) -3.72 (152), -12.25 (129), -47.31 (177), -92.70‘ (C0)~Cr(PhCHz)zCzB4H6 (5) -1.61: -4.06 (146), 1:2:1 -47.65 (176) ( C O ) B C ~ Z ( P ~ C H ~ ) ~(6) C ~ B , H-8.91,’ ~ -10.79 (1321, 1:2:1 -54.9 (178)
CHzClz solution. downfield.
Shifts relative to BF3.Et20, positive value
‘Unresolved doublet.
Table 11. 360-MHz ‘H FT NMR Data compd p b 1 7.28 m ( C a s ) , 2.68 m (BH),’ 2.31 m (CH2), 1.32 m (BHB) 2 7.25 m (CeH,), 1.28 m (CHJ, -10.51 s (FeH) 3 7.21 m (CeH,), 1.28 m (CHz) 5 7.30 m, br (C6H6),2.42 m (BH), 2.18 m (CH,), 1.27 m (BHB) 6 7.38 m (CBH6),2.46 m (BH), 2.25 m (CHz), 1.18 m (BHB)
re1 areas 5:2:2:1
10:4:1 5:2 5:4:2:1 5:4:2:1
‘CDClS solution. bShifts relative to Me4Si. Legend: br = broad, m = multiplet, s = singlet. ‘Terminal B-H quartets are broad and in most cases are partially or wholly obscured by C-H signals.
Table 111. Infrared Absorptions (cm-’, KBr Pellets)n compd
I*
2
3
5
6
absorptions 3165 ah, 3100 m, 3080 8,3022 s, 2972 sh, 2938 s, 2864 s, 2608 vs, 1948 m, 1610 8,1592 sh, 1501 vs, 1460 vs, 1388 w, 1115 m, br, 1082 m, 1037 sh, 987 m, 960 m, 921 w, 892 sh, 855 m, 822 w, 794 m, 752 s, 732 s, 704 vs 3105 w, 3084 m, 3050 m, 2944 s, 2868 m, 2622 s, 2600 s, 1611 w, 1505 m, 1462 m, 1082 m, 1038 m,988 w, 755 w, 730 w, 708 m, 480 w 3062 w, 3040 w, 3005 w, 2900 m, 2881 w, 2838 m, 2580 m, 2562 m, 2536 s, 2502 m, 1590 m, 1482 s, 1440 s, 1422 m, 1379 w, 1294 m, 1174 w, 1142 w, 1068 m, 1018 m, 1002 m, 990 w, 979 w, 958 w, 872 m,742 m,712 m, 688 s, 628 w, 530 w, 449 w 3104 w, 3084 w, 3050 w, 2942 vs, 2878 vs, 2622 vs, 1958 vs, br, 1898 vs, br, 1614 w, 1508 m, 1468 m, 1390 w, 1088 w, 1038 w, 758 w, 742 w, 738 w, 710 m,675 m, 640 m, 542 m,488 w 3115 m, 2920 m,2618 8,2608 m, 2600 m, 1920 vs, br, 1742 vs, br, 1460 m, 1431 m, 1168 w, 980 w, 950 w, 858 w, 836 w, 812 w, 770 w, 750 w, 691 w, 668 s, 637 s, 538 s, 482 m, 400 w, 312 m
‘Legend sh = shoulder, m = medium, s = strong, v = very, w = weak, br = broad. bNeat sample.
resemble, in general, those of its tetra-C-alkyl counter(R2C2B4H4l2FeH2 (R = Me, Et, i-Pr), and 2 is assumed to adopt a similar bis(carborany1)iron sandwich structure. Of course, the relative conformation of the two carborane ligands may or may not be identical with that previously established in (Me2C2B4H4)2FeH2, whose ligands are rotated by 90° relative to an eclipsed orientation.I2 (11)Maynard, R. B.; Grimes, R. N. Inorg. Synth. 1983,22,215. (12)Pipal, J. R.; Grimes, R. N. Znorg. Chem. 1979,18, 263.
T-
Organometallics, Vol. 6, No. 2, 1987 337
Complexation of nido- (PhCH2)2C&4H6 Table IV. Selected Mass Spectroscopic Data assignt compd mfe re1 intensit9 13C12C 1lB 1H + 1 257 16.2 15 4 20 2
178 91 567 556 565 564 563 562 561 508 507 506 505 255 176 91 509 508 507 506 505 504 255 91 688 687 686 685 684 683 509 508 507 506 505 255 91 393 392 391 390 389 308 307 306 305 255 91 529 528
18.9 88.5 0.3 (1.1) 2.9 (3.7) 5.4 (5.4)
1
parent - C6H6 C&,CH2+ 13C12C3111B856Fe'H38t
Table V. Experimental Parameters and Crystal (PhCHd&4Ba& (3) Mr 507 D(calcd), g space group R1/c 28 range, deg reflctns obsd a, A 10.007 (2) b, A e, A & deg
22.681 (6) 13.692 (2) 110.18 (2) 2917 4.5
v, A3
fi,
1.5 (0.8) 0.8 (0.2) 7.9 (10.7) 1 15.6 (15.6) 15.1 (11.9) 1C32B8H36' 11.1 (5.4) J 100.0 (C&,CHZ)ZC~B~HS' 97.2 68.6 CsHbCH2' 6.2 (6.7) 13C12C 31"B 8'H 38
cm-'
reflctns refined
R R, esd unit w t
z
radiation
Data on 1.155 1-116 4501 3813 0.053 0.056 1.1 4 cu
Values in parentheses are calculated intensities for the parent (or other) group, based on natural isotope abundance5 and normalized to the most intense observed peak in the group.
with the expectation (vide supra) that oxidative fusion would be sterically impeded by the benzyl groups. However, solutions of 2 in CH2C12or benzene on standing overnight in air gave the tetra-C-benzyl carborane (PhCH2)4C4B8H8 (3) in 48% yield as colorless nonvolatile air-stable crystals (Scheme I). From its l'B and lH NMR and mass spectra, 3 was identified as a C4B8cluster of the same class as the crystallographicallycharacterized species Me4C4B8H8'3and Et4C4B8H,.10 The llB spectrum of 3 is particularly suggestive of an open-type geometry as found in the tetraethyl derivative; since the detailed cage geometry is of interest for reasons mentioned earlier, an X-ray structure determination was undertaken. Solid-state Structure of (PhCH2),C4B8H8 (3). Tables V-VI11 list crystallographic data collection parameters, final positional parameters, bond distances, and bond angles, with corresponding lengths in Et4C4B8H8included for comparison (tables of thermal parameters and calculated mean planes and a packing diagram are available as supplementary material). The C4B8cage structure, depicted in Figure l , is of type "B"'O and surprisingly is virtually identical with that of the tetraethyl derivative, as shown by comparison of bond distances (Table VII). A further point of comparison is given by the dihedral angle formed by the C243-B4-B5-B6 and C748-B+BlO-Bll planes, which is 27.4O in 3 and 28.2' in Et4C4B8H8. The phenyl rings in 3 are planar within experimental error, but their orientation in the crystal is worthy of comment. As can be seen in Figure 1, each pair of benzyl groups (those bonded to adjacent cage carbon atoms) is positioned such that its phenyl rings are roughly perpendicular to each other, with a C-H bond on one ring directed approximately toward the center of the other ring of the pair. This appears to be a crystal packing effect since the closest inter-ring contacts within each pair of benzyl groups correspond to van der Waals distances or greater (Table XIII, supplementary material). Solution Behavior of (PhCH2),C4B8Hs.As noted above, R4C4B8H8carboranes in which R = CH3, C2H5,or n-C,H, exhibit cage fluxionality in solution (essentially independent of solvent), with "open" (B) and "closed" (A) structures present in equilibrium in each case. The AH values for A B conversion are quite small (ca. 1-2 kcal mol-'), but the equilibrium is shifted toward the open form as the size of the R groups increases.l0 It was of interest to see whether such behavior is maintained in the tetrabenzyl derivative 3, and accordingly we examined the llB and 'H NMR spectra as a function of time. In both experiments there is no evidence of change on a time scale of weeks a t room temperature, nor do the spectra give any indication of more than one isomer. Hence we conclude
In contrast to the corresponding methyl-, ethyl-, and n-propylcarborane iron complexes, which react with atmospheric O2within minutes to give R4C4B8H8,2 survives exposure to air for 1-2 h with little change. This is in line
(13) (a) Freyberg, D. P.; Weiss, R.; Sinn, E.; Grimes, R. N. Inorg. Chem. 1977,16,1847. (b) Grimes, R. N.; Maxwell, W. M.; Maynard, R. B.; Sinn, E. ibid. 1980, 19, 2981.
3
4
5
6
527 526 525 445 444 443 442 441 360 358 308 91
+
5.2 100.0 4.6 (3.2)
(C~HSCH~)~C~B~H~+ CeH6CH2' 12C3711B85BFe5sCo'H41t
47.6 100.0 0.7 (0.6) 2.1 (2.1)
(C&CHz)zCzB4H6' CeH5CHz'
13C1ZC1811B~e0352Cr1H2~*
1
1.2 (0.7) 0.3 (0.2) 11.4 \ 13s7 )parent - 3 co envelope 9.1 2.6 J 100.0 parent - Cr(C0)3H 100.0 C&,CH2' 10.3 (10.2) 13C12C2111B4160852Cr~H20t 23.8 (23.8)
pi: [i:;)
4.2 (2.7) 10.6 26.7 26.6 17.5 8.9 14.8
700.0
36.8 98.9
parent - 3CO envelope
-+
)parent - 6CO 'parent - c ~ ( c o ) ~ C&,CH2'
338 Organometallics, Vol. 6, No. 2, 1987
Spencer et al.
Figure 1. Stereoview of (PhCH,),C4B,HB ( 3 ) Scheme I OC
OBH
I)NaH 2)Fe C Iz
-2
A
that 3 is nonfluxional, in contrast to the tetraalkyl derivatives studied previously (it should be noted that (Me3Si)zC4BsHlo, prepared by Hosmane and co-workers,14 is also apparently nonfluxional). The solution properties of 3 may to some extent reflect the electronic influence of the benzyl groups on the C4Bsframework; however, such an effect must be relatively minor in view of the nearly identical solid-state cage structures of 3 and its tetraethyl counterpart.1° Consequently, we attribute the nonfluxionality of 3 primarily to the steric interaction of the benzyl substituents which effectively "freeze" the cage into an open configuration. Examination of models supports this conclusion, since it is apparent that "closuren of the cage via formation of a C3-C7 bond (as in the methyl, ethyl, and propyl analogues)1° would, in the case of 3, produce substantially increased crowding of the benzyl units. We anticipate further testing of this effect as other R4C4B8H8 species with bulky R groups are examined. The 360-MHz 'H NMR spectrum of 3 indicates that the four benzyl units are equivalent on the NMR time scale, implying that the ordering of the phenyl rings in the crystal
(14) Hosmane, N. S.;Dehghan, M.; Davies, S. J.Am. Chem. SOC.1984, 21, 6435.
is not maintained in solution and, as suggested earlier, is strictly a solid-state feature. Reaction of 2 with (V~-C~H~)CO(CO)~. Given that the bulky benzyl substituents in 2 do not prevent formation of the C4B8carborane 3 via ligand fusion, it was of interest to examine the reactivity of 2 toward metal-inserting reagents. T h e tetra-C-methyl counterpart of 2, (Me2CzB4H4)zFeHZ, is known to react photolytically with ( V ~ - C J ~ ~ ) C O (to CO ) ~ (C5H5)Cointo the cage;15in this insert work, similar treatment of 2 with (v5-C5H5)Co(C0),gave a single isolable product which was characterized as [ (PhCHz)ZC,B4H4]ZFeCo(q5-C5H5) (4). From its llB, lH, and mass spectra, 4 was deduced to be structurally analogous to the compound (MeZCZB4H4)zFeCo(v6-C5H5), which exhibits a "wedged" geometry in which the iron atom is sandwiched between C2B4and CoCzB, ligands with a BH unit located in the interligand crevice (Scheme I).16 This observation further underlines the impression that the general reactions established for nido-&CzB4H, carboranes proceed even when R is as sterically demanding (and (15) Maxwell, W. M.; Miller, V. R.; Grimes, R. N. Inorg. Chem. 1976, 15, 1343. (16) Maxwell, W. M.; Sinn, E.; Grimes, R. N. J.Am. Chem. SOC.1976, 98, 3490.
Organometallics, Val. 6, NO.2, 1987 339
T-Complexation of nido- (PhCH2)2Cfi&6 Table VI. Positional Parameters for (PhCH*),C,BaHa (3) atom
x ~
c3 c7 C8
c21 c22 C23 C24 C25 C26 C27 C31 C32 c33 c34 c35 C36 c37 C71 C72 c73 c74 c75 C76 c77 C81 C82 C83 C84 C85 C86 C87 B1 B4 B5 B6 B9 B10 B11 B12 H1 H4 H5 H6 H9 H10 H11 H12 H211 H212 H23 H24 H25 H26 H27 H311 H312 H33 H34 H35 H36 H37 H711 H712 H73 H74 H75 H76 H77 H8ll H812 H83 H84 H85 H86 H87
0.390292 0.265173 0.198551 0.108623 0.484625 0.564933 0.544253 0.618517 0.708727 0.733052 0.660594 0.201903 0.175892 0.286473 0.262134 0.128430 0.017070 0.040452 0.146543 0.195234 0.127944 0.167391 0.277638 0.347392 0.306362 -0.051499 -0.135460 -0.137218 -0.215836 -0.293545 -0.295288 -0.216296 0.381872 0.192073 0.333207 0.455734 0.178693 0.354798 0.357784 0.211244 0.444381 0.102260 0.358363 0.576581 0.097366 0.412586 0.445902 0.167141 0.546573 0.425587 0.481529 0.603003 0.762910 0.819176 0.671449 0.267125 0.105221 0.381713 0.348327 0.106949 -0.068557 -0.044328 0.031123 0.181248 0.049912 0.097920 0.3 17562 0.437941 0.361931 -0.089586 -0.068721 -0.084578 -0.236082 -0.368650 -0.350971 -0.207720
Y 0.332768 0.366172 0.252455 0.296261 0.312598 0.361439 0.373396 0.420228 0.454662 0.442554 0.395892 0.383443 0.449020 0.486285 0.546032 0.568244 0.532089 0.47'1596 0.205008 0.143443 0.112248 0.055017 0.029095 0.059383 0.116865 0.299488 0.250610 0.244871 0.199438 0.160089 0.166873 0.211784 0.399597 0.382948 0.377152 0.331412 0.333000 0.301637 0.258633 0.254993 0.441216 0.416399 0.410701 0.329696 0.349341 0.291348 0.225019 0.219596 0.284851 0.290578 0.349109 0.428378 0.485164 0.463301 0.387420 0.370184 0.362694 0.470201 0.571000 0.616789 0.548795 0.441284 0.204314 0.215992 0.129815 0.030777 -0.015697 0.038409 0.141437 0.341138 0.300553 0.280063 0.199404 0.126489 0.137747 0.216582
z -0.029765 -0.072751 -0.011955 0.006048 -0.089948 -0.119030 -0.223448 -0.248152 -0.172493 -0.069209 -0.043194 -0.186498 -0.204094 -0.198971 -0,219968 -0.243916 -0.247972 -0.228242 -0.095508 -0.057077 -0.000536 0.031950 0.008578 -0.047287 -0.079715 -0.050083 -0.023978 0.077765 0.101813 0.024806 -0.076044 -0.100462 0.031451 0.009035 0.136473 0.098558 0.115679 0.172416 0.060328 0.113508 0.031349 -0.009202 0.200886 0.137424 0.148947 0.255727 0.072208 0.157908 -0.052741 -0.157485 -0.272730 -0.323585 -0.184446 -0.018762 0.027005 -0.223026 -0.218330 -0.180718 -0.215264 -0.263439 -0.252783 -0.229915 -0.130902 -0.153893 0.011864 0.068382 0.030824 -0.064466 -0.118486 -0.038071 -0.118570 0.136066 0.183917 0.043336 -0.133682 -0.179418
Table VII. Bonded and Nonbonded Distances (A) in 3 ( P h C H d 4 C W b (3)
Et4C4BBHBa
~
C2-C3 c2-c21 C2-B1 C2-B6 C2-Bll C3-C31 C3-B1 C3-B4 C7-C8 C7-C71 C7-Bll C7-Bl2 C8-C81 C8-B4 C8-B9 C8-Bl2 Bl-B4 B1-B5 BI-B6 B4-B5 B4-B9 B5-B6 B5-B9 B5-BlO B6-BlO B6-Bll B9-BlO B9-Bl2 B 10-B11 BlGB12 Bll-B12 c21-c22 C22-C23 C23-C24 C24-C25 C25-C26 C26-C27 C27-C22 C31-C32 C32-C33 c33-c34 c34-c35 C35-C36 C36-C37 C37-C32 C71-C72 C72-C73 c73-c74 c74-c75 C75-C76 C76-C77 C77-C72 C81-C82 C82-C83 C83-C84 (284485 C85-C86 C86-C87 C87-C82 C2-C7 c347 C3-C8
Bond Distances 1.407 (1) 1.522 (2) 1.748 (2) 1.650 (2) 2.175 (3) 1.516 (3) 1.681 (3) 1.581 (2) 1.418 (1) 1.525 (2) 1.565 (2) 1.679 (3) 1.521 (2) 2.131 (2) 1.647 (2) 1.747 (2) 1.855 (2) 1.746 (2) 1.820 (2) 1.832 (2) 1.889 (2) 1.813 (2) 1.781 (3) 1.775 (2) 1.790 (2) 1.899 (3) 1.808 (2) 1.801 (2) 1.827 (2) 1.742 (2) 1.850 (3) 1.501 (2) 1.399 (2) 1.403 (2) 1.361 (1) 1.377 (1) 1.397 (2) 1.385 (3) 1.515 (3) 1.375 (2) 1.389 (2) 1.360 (3) 1.369 (2) 1.402 (2) 1.378 (3) 1.512 (3) 1.383 (2) 1.385 (3) 1.382 (2) 1.383 (3) 1.393 (2) 1.391 (3) 1.507 (2) 1.405 (3) 1.403 (2) 1.395 (3) 1.384 (2) 1.399 (2) 1.394 (2) Nonbonded 2.717 2.858 2.703
Distances (1) (1) (1)
1.362 (6) 1.506 (7) 1.732 (8) 1.627 (6) 2.181 (6) 1.554 (5) 1.669 (6) 1.603 (8) 1.408 (7) 1.502 (7) 1.574 (6) 1.656 (7) 1.530 (6) 2.145 (7) 1.672 (7) 1.763 (6) 1.859 (7) 1.737 (8) 1.825 (7) 1.832 (6) 1.878 (6) 1.867 (9) 1.788 (6) 1.809 (7) 1.790 (7) 1.859 (6) 1.857 (7) 1.840 (8) 1.744 (8) 1.712 (7) 1.804 (9)
2.743 (7) 2.886 (2) 2.702 (7)
Reference 10.
electronically active) as benzyl. However, current work in our laboratory indicates that still larger R groups have a more pronounced effect on the properties of R2C2B4H6 carboranes, in some cases even preventing formation of a (RzC2B4H,)2FeH2 complex altogether." (17) Spencer, J. T.; Fessler, M. E.; Grimes, R. N., to be submitted for publication.
340 Organometallics, Vol. 6, No. 2, 1987 Table VIII. c3-c2-c21 C3-C2-B1 C3-C2-B6 C3-C2-B11 C2 1-C2-B 1 C21-C2-B6 C2142-Bll Bl-C2-B6 B 1-C2-B 11 B6-CZ-Bll c2-c3-c31 C2-C3-B 1 C2-C3-B4 C31-C3-B1 C31-C3-B4 Bl-C3-B4 C8-C7-C71 CEI-C'i-Bll C8-C7-B 12 C71-C7-Bll C7 1-C 7-B12 B1l-C7-B12 C7-C8-C81 C7-CS-B4 C'i-C8-B9 C7-C8-B12 C81-C8-B4 C81-C8-B9 C8l-C8-B 12 B4-C8-B9 B4-C8-B 12 B9-C8-B12 c23-c22-c27 c23-c22-c21 c27-c22-c21 c22-c23-c24 c23-c24-c25 C24-C25-C26
Spencer et al.
Selected Bond Angles (deg) in 3 124.3 (2) 63.3 (1) 115.1 (2) 111.6 (2) 131.4 (2) 118.6 (2) 108.5 (2) 64.7 (1) 110.9 (1) 57.6 (1) 124.4 (2) 68.3 (1) 113.3 (2) 132.6 (2) 122.3 (2) 69.3 (2) 123.5 (2) 113.3 ( 2 ) 68.1 (1) 123.2 (2) 132.6 (2) 69.4 (2) 124.5 (2) 112.4 (2) 114.6 (2) 63.1 (1) 107.6 (2) 118.6 (2) 131.4 (2) 58.3 (1) 111.4 (2) 64.0 (1) 118.5 (2) 120.7 (2) 120.8 (2) 119.3 (3) 121.2 (3) 120.2 (3)
C25-C26-C27
119.3 (3) 131.4 (3) 113.9 (2) 120.3 (2) 120.2 (2) 119.4 (2) 120.6 (2) 119.9 (3) 120.5 (2) 119.9 (3) 119.7 (3) 113.9 (2) 120.4 (2) 120.6 (2) 119.0 (2) 121.3 (3) 119.1 (3) 128.8 (2) 119.5 (3) 120.3 (2) 114.9 (2) 120.1 (2) 120.9 (2) 118.9 (2) 120.0 (3) 120.3 (3) 119.7 (3) 120.4 (3) 120.7 (2) 114.2 (2) 92.2 (1) 105.3 (2) 98.3 (2) 103.6 (2) 103.8 (2) 98.3 (2) 91.7 (1) 105.7 (2)
Reaction of 1 w i t h Chromium Hexacarbonyl. The ability of the phenyl rings in 1 to adopt q6-coordination with Cr(C0)3was examined by refluxing the carborane with CI-(CO)~ in tetrahydrofuran-dibutyl ether, forming two orange crystalline products, 5 and 6, which were isolated in 51% total yield. Characterization by NMR, IR, and mass spectroscopy supported by an X-ray study of 6, identified the new compounds as a monochromium complex, 2- [ (C0)3Cr(~6-C6H5)CH2]-3-(PhCHz)-2,3-C2B4H6 (51, and a dichromium species, 2,3-[ (C0)3Cr(q6-C6H5)CH2]z2,3-C2B4H6(6). The latter compound was also produced by reaction of 5 with Cr(CO)6 (Scheme I). The 115.5-MHz IlB NMR spectra of 1, 5, and 6 are similar, each exhibiting three signals in a 1:2:1 area ratio (typical of nido-R2CzB4H6derivatives). In the spectra of the metalated species 5 and 6, all three resonances exhibit upfield shifts relative to uncomplexed 1; the effect is particularly evident in the dimetallic species 6 where the signals are found ca. 8 ppm to high field of 1. The highresolution proton NMR spectra of the three compounds are almost identical, with little shift (0.02-0.10 ppm) detectable in the chromium-complexed phenyl rings relative to the parent carborane; in contrast, the complexation of arenes with Cr(C0)3normally causes an upfield shift of 1.5-2.5 ppm.ls The virtual absence of such an effect in 5 and 6 indicates that the CzB4 carboranyl unit essentially neutralizes the influence of the Cr(C0)3 groups on the phenyl rings (implying substantial carborane-phenyl electronic interaction). Moreover, it is likely that the effects of metalation are buffered by electron delocalization across the large dibenzylcarborane system. (18) For a recent review see: SolladiB-Cavallo,A. Polyhedron 1985, 4 , 901.
Table IX. Experimental Parameters and Crystal Data on (CO)fiCr2(PhCH2)2C2BdHfi (6) 521 28 range, deg 4-55 Mr space group Pnam reflctns obsd 3979 8, b, 8, a, c,
A
v, A3
1,cm-' D(calcd), g cm-3
11.914 (2) 6.927 (1) 28.729 (6) 2371 (1) 9.283 1.458
reflctns refined
R Rw esd unit wt
z
radiatn
1678 0.044 0.048 1.4 4 Mo K a
In contrast to the parent carborane 1, complexes 5 and 6 are air-sensitive in solution and revert to 1; however, in the solid state both compounds appear to change only very slowly on prolonged exposure to light, air, and moisture. These properties are fairly typical of arene-chromium tricarbonyl complexes as a class. X-ray Crystallographic S t u d y of 6. Perhaps surprisingly given the extensive synthetic effort in this area, no crystal structure of a simple (o-bonded only) derivative of nido-2,3-C2B4H,has been reported since the original X-ray investigations of the parent molecule and 2,3Me2-2,3-C2B4H6 by Lipscomb and co-workers more than 20 years (Structures of the bridged complexes p(4,5)-X-2,3-R2C2B4H5where X = (Et3P),PtH20 and (C5H,)Co(Me2C2B4HJ21have been reported, and the geometry of 2-Me3Si-2,3-C2B4H7has been studied by gasphase electron diffraction.22) In view of the paucity of detailed structural information on uncomplexed R2C2B4H6 carboranes and also in order to examine the consequences of $-metal coordination a t the phenyl rings, we undertook an X-ray diffraction investigation of the dichromium complex 6. The parameters of data collection, atomic coordinates, and bond distances and angles are given in Tables JX-XII, and drawings of the molecular structure of 6 are given in Figure 2; tables of thermal parameters and calculated mean planes are available as supplementary material. The molecule has crystallographically imposed mirror symmetry and is consistent with the structure indicated from NMR data. The C2B4cage structure is closely comparable to those of the parent and dimethyl species,19there being no significant differences in framework bond distances. The phenyl ring is planar within experimental error and the C6H,-Cr(CO)3 group displays bond lengths and angles within the normal ranges for monosubstituted arenechromium tricarbonyl complexes,23but the orientation of the Cr(C0)3unit is staggered with respect to the attached phenyl ring. This observation runs counter to the usual prediction based on electronic considerations for monosubstituted ( ~ ~ - a r e n e ) C r ( C Ocomplexes, )~ in which one normally finds the carbonyls eclipsing three of the ring carbons.23 Undoubtedly the departure of 6 from this rule is related to the large steric bulk of the -CH2-carborane substituent, an effect that has been noted in a few previously studied complexes (e.g., [ (C,H5)Cr(CO)3]z24), where intramolecular contacts force the molecule to adopt a staggered conformation. There is also evidence of an
(19) Boer, F. P.; Streib, W. E.; Lipscomb, W. N. Inorg. Chem. 1964, 3, 1666.
(20) Barker, G. K.; Green, M.; Stone, F. G. A.; Welch, A. J.; Onak, T. P.; Siwapinyoyos, G. J. Chem. Soc., Dalton Trans. 1979, 1687. (21) Borelli, A. J., Jr.; Plotkin, J. S.; Sneddon, L. G. Inorg. Chem. 1982, 21, 1328. (22) Hosmane, N. S.; Maldar, N. N.; Potts, S. B.; Rankin, D. W. H.; Robertson, H. E. Inorg. Chem., in press. (23) Muetterties, E. L.; Bleeke, J. R.; Wucherer, E. J.; Albright, T. A. Chem. Reu. 1982, 82, 499. (24) Corradini, P.; Allegra, G. J. Am. Chem. SOC.1960, 82, 2075.
Organometallics, Vol. 6, No. 2, 1987 341
7-Complexation of nido- (PhCH2),C&H6
Table X. Positional Parameters for (CO)sCr2(PhCH2)2C2B4H6 (6) atom 2 Y I:
atom
X
Cr 01 02 03 C1R C2R C3R C4R C5R C6R CW) c2 c11 c12 C13
0.17471 (4) 0.0178 (2) 0.3293 (2) 0.0646 (3) 0.2302 (3) 0.3166 (3) 0.2986 (3) 0.1965 (4) 0.1084 (3) 0.1255 (3) 0.2468 (4) 0.2732 (3) 0.0772 (3) 0.2690 (3) 0.1073 (3)
0.12975 18) 0.2952 ( 5 ) 0.4588 (4) 0.3679 (5) -0.0821 ( 5 ) -0.0530 ( 5 ) -0.0778 (6) -0.1330 (6) -0.1631 (6) -0.1392 ( 5 ) -0.0536 (6) -0.2388 ( 5 ) 0.2300 (6) 0.3317 ( 5 ) 0.2756 (6)
0.09438 (2) 0.02354 igj 0.0737 (1) 0.16816 (9) 0.1475 (1) 0.1161 (1) 0.0677 (1) 0.0513 (1) 0.0822 (1) 0.1298 (1) 0.1990 (1) 0.2252 (1) 0.0510 (1) 0.0818 (1) 0.1396 (1)
B6 B5 B1 HB6 HB5 H2R H3R HB1 H4R H5R H6R HB56 HM1 HM2
0.3294 (4) 0.3761 (7) 0.4013 (6) 0.355 (3) 0.435 (4) 0.376 (2) 0.354 (3) 0.476 (4) 0.181 (3) 0.044 (3) 0.065 (2) 0.296 (3) 0.179 (3) 0.292 (3)
Y -0.4126 (6) -0.555 (1) -0.312 (1) -0.429 (5) -0.684 (7) -0.017 (4) -0.050 ( 5 ) -0.226 (7) -0.156 ( 5 ) -0.196 ( 5 ) -0.151 (4) -0.576 ( 5 ) -0.004 ( 5 ) 0.064 ( 5 )
z
0.2027 (1) 0.250 0.250 0.169 (1) 0.250 0.1266 (9) 0.051 (1) 0.250 0.018 (1) 0.071 (1) 0.148 (1) 0.218 (1) 0.211 (1) 0.206 (1)
Table XI. Interatomic Distances (A) in 6 Cr-ClR Cr-C2R Cr-C3R Cr-C4R Cr-C5R Cr-C6R Cr-C11 Cr-Cl2 Cr-C13 01-Cll 02-c12 03-C13 C 1R-C 2R
2.219 (3) 2.203 i3j 2.199 (4) 2.216 (4) 2.205 (4) 2.202 (4) 1.840 (3) 1.830 (4) 1.831 (4) 1.152 (3) 1.160 (4) 1.158 (4) 1.383 (5)
C1R-C6R C1R-C (M) C2R-C3R C2R-H2R C3R-C4R C3R-H3R C4R-C5R C4R-H4R C5R-C6R C5R-H5R C6R-H6R C(M)-C2 C(M)-HMl
Table XII. Selected Bond Angles (deg) in 6 C11-Cr-C12 C11-Cr-Cl3 C12-Cr-C13 Cr-C 1R-C (M) C2R-ClR-C(M) C6R-C lR-C(M) C2R-C1R-C6R ClR-CPR-C3R C2R-C3R-C4R C3R-C4R-C5R C4R-C5R-C6R ClR-CGR-C5R ClR-C(M)-CB C1R-C(M)-HM1
88.0 (2) 89.7 (1) 89.3 (1) 128.9 (2) 121.6 (4) 120.6 (4) 117.8 (3) 120.6 (3) 120.6 (3) 119.8 (3) 119.9 (4) 121.3 (3) 113.7 (2) 107 (2)
ClR-C(MbHM2 C2-C (M)-HM1 C2-C (M)-HM2 HMl-C(M)-HMP C(M)-C2-B6 C(M)-C2-B1 C2'-C2-B6 C2-B6-B5 B6-B5-B6' B6-HB56-B5 Cr-C11-01 Cr-C12-02 Cr-C13-03
113 (2) 108 i2j 118 (2) 95 (3) 123.4 (4) 128.7 (4) 115.1 (3) 104.6 (3) 100.4 (3) 85 (2) 178.6 (3) 179.5 (3) 180.00 (0)
electronic effect by the -CH2-carborane group on the c6 ring, in that a smaller internal C-C-C angle is found on the substituted ring carbon C1R [117.8 (31'1 than on the remaining ring atoms [mean value 120.4 (l)']. The chemical properties of the mono- and dimetalated complexes 5 and 6 are of particular interest, since they offer an opportunity to study the consequences of coordinating strongly electron-withdrawing Cr(C0)3units to the dibenzylcarborane 1. An investigation of these and related complexes is in progress.
Conclusions This work demonstrates that the C,C'-dibenzyl-nidocarborane 1, like its alkylated analogues R2C2B4H6(R = CH,, C2H5,or n-C3H7),4can be converted to a complex (&C2B4HJ2FeH, which in turn undergoes oxidative fusion to form the tetra-C-benzyltetracarbon carborane 3; the insertion of (q5-C6H5)Cointo the framework of 1 also parallels earlier observation^,'^ generating a wedged dimetallacarborane 5. However, effects arising from the presence of the four C-benzyl substituents are clearly evident in the cage nonfluxionality of 3 and also in the
1.404 (5) 1.506 (4) 1.419 (5) 0.81 (3) 1.359 (5) 0.83 (3) 1.390 (5) 0.98 (4) 1.391 (5) 0.86 (3) 0.89 (3) 1.520 ( 5 ) 0.95 (3)
C(M)-HMP C2-B6 C2-B1 C2-C2' C6-B5 C6-B1 B6-HB6 B6-HB56 B5-B1 B5-HB5 B5-HB56 Bl-HB1
1.00 (4) 1.521.(5) 1.760 (7) 1.424 (5) 1.468 (6) 1.750 (6) 1.02 (3) 1.28 (4) 1.704 (9) 1.13 ( 5 ) 1.33 (3) 1.08 (5)
relatively sluggish fusion (compared to its alkyl analogues) of 2 to give 3. These findings suggest that substituents larger than benzyl might produce more dramatic effects, such as failure of the fusion reaction altogether. Current studies in our laboratory involving carboranes with attached indenylmethyl and fluorenylmethyl groups tend to support this idea and will be described later.
Experimental Section Materials. Except as noted, all reagents and solvents used were as given in an accompanying paper.3a nido-2,3-Dibenzyl2,3-dicarbahexaborane@)(1) was prepared as described elsewhere.' Cyclopentadienylcobaltdicarbonyl and chromium hexacarbonyl were used as received from Strem Chemicals, Inc. Instrumentation. The instruments and procedures employed in this work have been described previou~ly.~~ Preparation of [(PhCH2)2C2B4H4]2FeH2 (2). A solution of (PhCH2)2C2B4H5was prepared from the reaction of 0.68 g (2.7 mmol) of 1 and 0.15 g (6.3 mmol) of NaH in 35 mL of anhydrous THF at 0 OC by using the procedure previously given' and employing an apparatus similar to that described elsewhere.% After being stirred at room temperature for 1h, this solution was filtered into 0.18 g (1.4 mmol) of anhydrous FeC1, in a 100-mL flask immersed in a dry ice-acetone slush bath. The reaction mixture was stirred for 2 h at this temperature and then slowly warmed to room temperature followed by stirring for an additional 15 min. The solvent was quickly removed in vacuo, and the resulting dark red residue was transferred to a glovebox under dry N2 and dissolved in 40 mL of dry benzene. This solution was filtered through a 2-cm layer of silica gel on a sintered glass frit and washed with additional benzene until the washings were colorless. The benzene was removed in vacuo and the residue sublimed at 70 "C and torr. The red compound, which was collected on a cold finger at -78 OC, gave 0.54 g (0.96 mmol, 72% yield) of 2 as an air-sensitive, red solid. Conversion of 2 to (PhCH2),C4B8Hs(3). In an apparatus similar to that previously described,%0.78 g (1.38 mmol) of 2 was (25)Maynard, R. B.; Borodinsky, L.;Grimes,R. N. Znorg. Synth. 1983, 22, 215.
342 Organometallics, Vol. 6, No. 2, 1987
Spencer et al.
\ i Figure 2. Views of ( C O ) 6 C r z ( P h C H ~ 2(6): c ~ 4top, ~ molecular
structure; bottom, (C0)3Cr($-C6HS)CHzgroup normal to plane of c6 ring.
dissolved in 40 mL of methylene chloride and O2gas was bubbled through the solution for 30 min. After subsequent exposure to air for 12 h, the solution was filtered in air and the solvent removed by rotary evaporation. The white residue was recrystallized from methylene chloride to give 0.70 g (48% yield) of 3 as air-stable, colorless crystals. [(PhCH2)2C2B4H4]2FeCo(qs-C5H5) (4). A 0.62-g (1.1-mmol) were sample of 2 and 0.31 g (1.7 mmol) of (~s-CsH5)Co(CO)2 dissolved in 100 mL of dry degassed benzene, and the solution was placed in an Ace Glass Co. quartz photochemical reactor employing a 450-W mercury vapor lamp. Under a dry nitrogen atmosphere, the solution was irradiated for 5 h with constant stirring. The reactor was opened to the atmosphere and the solution filtered through silica gel, washing with methylene chloride. The solvent was removed by rotary evaporation to yield a dark orange solid, which was chromatographedon silica gel TLC plates and developed with 955 CH2C12-hexane to give 0.19 g (28% yield) of dark red crystalline 4 ( R 0.80). Preparation of (C0)3Cr(~hCH2)2C2B4H6 (5) and (CO)&r2(PhCH2)&&& (6). Into a 250-mL round-bottomflask equipped with a condenser and magnetic stirrer were placed 0.572 g (2.23 mmol) of (C6H5CH2)2C2B4H6 and 2.47 g (11.2 mmol) of chromium hexacarbonyl. Anhydrous dibutyl ether (45 mL) and 5 mL of anhydrous tetrahydrofuran (THF) were added, and the reaction mixture was refluxed under dry Nz for 18 h. The reactor was cooled to room temperature y d filtered and the solvent removed in vacuo. The residue was extracted with methylene chloride and chromatographed on silica gel preparative TLC plates with a 2:3 CH&-hexane solution. Two orange bands were collected, the first of which (Rf0.51 in 2 3 CH2C12-hexane)gave 0.283 g (32.4% yield) of 5. The second band (Rf0.28) provided 0.219 g (18.6% yield) of 6. Both complexes are orange, crystalline, moderately air-stable materials, decomposing only slowly on exposure to the air. The dimetallic complex 6 was also prepared by the reaction of 5 with a 1 O : l excess of Cr(CO)6in 1 O : l refluxing dibutyl eth-
er-THF solution under dry nitrogen. In a typical experiment, 0.374 g (0.954 mmol) of 5 was refluxed for 30 h with 2.09 g (9.50 mmol) of Cr(CO)6in 90 mL of anhydrous dibutyl ether and 10 mL of anhydrous THF. The product was chromatographically purified as previously described to yield 0.364 g of 6 (72.3% based on 2 employed). X-ray Structure Determination on (PhCH2)4C4B8H8 (3). Data were collected on a single crystal grown from CH2Cl2solution and mounted on a glass fiber, using standard methods on a Nicolet P3 four-circle diffractometer to determine cell dimensions and space group data. The 8-28 scan technique was employed as previously describedZ6vnto record the intensities for all nonequivalent reflections within the 28 range given in Table V. The intensities of three standard reflections showed no greater fluctuations during data collection than those expected from Poisson statistics. The raw intensity data were corrected for Lorentz-polarization effects but not for absorption. Only those reflections for which F,2 > 3a(F,2), where a(F,2) was estimated from counting statistics (p = 0.03),28were used in the final refinement of the structural parameters. The direct methods program MULTAN 74 was used to determine the non-hydrogen atom positions, and full-matrix leasbsquares refinement was carried out as previously described.% Anisotropic temperature factors were introduced for the nonhydrogen atoms. Further Fourier difference functions permitted location of all the hydrogen atoms, which were included in the least-squares refinement for several cycles and then held fixed. The model converged to the final R and R, values given in Table V, where R = ZllF, - F o l l / x F oand R, = ( ~ w ( F , ) ~ / Z W F , ~ ) ' / ~ . Tables of observed and calculated structure factors and thermal parameters are available as supplementary material. X-ray S t r u c t u r e Determination on (CO)6Cr2(PhCH2)2C2B4H6 (6). A single crystal of dimensions 0.2 X 0.3 X 0.4 mm, grown from CH2C12solution, was mounted in a random
orientation on the end of a glass fiber with epoxy cement and the fiber fixed to an aluminum pin with sealing wax and mounted on a goniometer head. Crystal data were obtained by standard procedure^^^ on a Nicolet P3m microprocessor-controlled diffractometer. Systematic absences of type hOO, h = 2n + 1,OkO, k = 2n + 1,001,1= 2n + 1,h01,h = 2n + 1,and Okl, k + 1 = 212 + 1, indicated possible space groups as Pna2, or Pnam (a nonstandard setting of Pnma). Data was collected by standard methods3, within the range 4" C 28 < 55". Solution and Refinement. The structure was solved by direct methods using a modified version of MULTAN 80, initially in the noncentric space group h 2 , . Positions of the two chromium atoms were located in an E map calculated from the highest combined figure of merit, and all subsequent non-hydrogen atoms were found from subsequent difference Fourier syntheses. At this point, careful analysis of chemically equivalent bond lengths indicated discrepancies, indicating that the centric space groyp Pnam was the correct choice. Positional parameters for the unique half-moleculewere then transformed to correspond to this space group. Subsequent refinement followed by difference Fourier syntheses revealed the positions of all hydrogen atoms. All non-hydrogen atoms were refined anisotropically, while hydrogen atoms were refined isotropically. In view of the regular shape of the crystal and the small value for the absorption coefficient, no absorption corrections were applied.
(26) Storm, C. B.; Freeman, C. M.; Butcher, R. J.; Turner, A. H.; Rowan, N. S.; Johnson, F. 0.; Sinn, E. Inorg. Chem. 1983,22, 678. (27) Nicolet P3/R3 Data Collection Manual; Calabrese, J. C., Ed.; Nicolet XRD Corp: Cupertinao, CA, 1980. (28) Corfield, P. W. R.; Doedens, R. J.; Ibers, J. A. Inorg. Chem. 1967, 6, 197. (29) Frevbera, D. P.: Mockler, G. M.: Sinn, E. J. Chem. SOC., Dalton Trans. 1976, 447.
(30) Brodsky,.N. R.; Nguyen, N. M.; Rowan, N. S.; Storm, C. B.; Butcher, R. J.: Smn, E. Inora. Chem. 1984.23, 891. (31) Programs used are p&t of the SDPiPlus Crystallographic Computing package supplied with the TEXRAY 234 Crystallographic Computing System. This is based on a PDP 11/73 computer with 1 megabyte of core storage, a Kennedy 800/1600 bpi magnetic tape drive, a SKYMNK array processor, an Envision color graphics terminal, an Envision color printer/plotter, and PDP 220 terminals.
Organometallics 1987, 6, 343-346
Acknowledgment. Support of this work by the National Science Foundation (Grant No. CHE 84-19401)and the Army Research Office is gratefully acknowledged. We thank Professor R. Bryan, University of Virginia, for 8ssistance in the X-ray data collection on compound 3. Registry No. 1, 105472-14-8;2, 105472-94-4;3, 105472-95-5; 4,105501-04-0;5,105472-92-2; 6,105472-93-3; (~5-CsHs)Co(CO),,
343
12078-25-0; Cr(CO)6, 13007-92-6.
Supplementary Material Available: Tables of structure factors, thermal parameters and calculated mean planes for compounds 3 and 6, a stereo diagram of unit cell packing for 3, and a table of short inter- and intramolecular nonbonded contacts in 3 (9 pages); listings of observed and calculated structure factors for 3 and 6 (34 pages). Ordering information is given on any current masthead page.
Variable-Temperature NMR Study of Dynamic Exchange in Sodium (p-Fluoro) bis(triethyla1uminate) James J. Harrison,*la David L. Beach,*lbDonald C. Young,” Kalkunte S. Seshadri, and John D. Nelligan Gulf Research & Development Company, P.O. Drawer 2038, Pittsburgh, Pennsylvania 15230 Recelved June 13, 1986
Variable-temperature 13C studies and ‘Hand 27AlNMR studies have been carried out on mixtures of Na[A12Et6F]and A12Eh. We observe that Na[A12EhF] undergoes facile exchange of A1Et3 with A12Eh in contrast to previously published work. The exchange process has been shown to involve a dissociative mechanism. A AH* of 20.4 kcal mol-’ (85.4 kJ mol-’) and AS*of 18.7 eu were determined. The value of AH* closely approximates the bond dissociation energy for the A1-F bond in Et3Al-F-AlEt3. This is the first reported bond dissociation energy for the A1-F bond in this unusual class of compounds. M[A12R6X] complexes2 (where M is alkali metal or tetraalkylammonium ion; X is halide, pseudohalide, or oxo anion; and R is an alkyl group) are of interest from the point of view of s t r ~ c t u r eelectronic ,~ properties,4 thermal behavior: and utilization in separating triethylaluminum from cr-olefins6and as “liquid clathrates”.‘ However, little, if any, fundamental thermodynamic bond data or kinetic data are available to aid in understanding the chemistry of these materials. In this paper, we report the ‘H, 13C, and 27AlNMR characterization of Na[A12Et6F]. Unexpectedly, we find that Na[A12Et6F]exchanges with A12Et6in toluene solution. The mechanism of exchange has been found to involve dissociation of Na[A12Et$] to Na[AlEbF] and ALE&. Examination of the activation energy for the exchange reaction yields a value for the Et3A1-F bond dissociation energy for this complex. Neat mixtures of Na[A12Pr6F]and A12Eh show little, if any exchange by 27Al NMR to form Na[A12Et6F] and A12Pr6a t 120 OC., However, i n toluene-d, a t room tem(1) (a) Chevron Research Co., P.O. Box 1627, Richmond, CA 94802. (b) Chevron Chemical Co. Kingwood Technical Center, 1862 Kingwood Drive, Kingwood, TX 77339. (2) Ziegler, K.; Koster, R.; Lemhkuhl, H; Reinert, K. Justus Liebigs Ann. Chem. 1960,629, 33-49. (3) (a) Allegra, G.; Perego, G. Acta Crystallogr. 1963,16,185-190. (b) Atwood, J. L.; Newberry, W. R., III J.Organomet. Chem. 1974,66,15-21. (c) Hrncir, D. C.; Rogers, R. D.; Atwood, J. L. J. Am. Chem. SOC.1981, 103,4277-4278. (d) Atwood, J. L.; Hrncir, D. C.; Rogers, R. D. J.Am. 1981, 103, 6787-6788. (e) Zaworotko, M. J.; Kerr, C. R.; Chem. SOC. Atwood, J. L. Organometallics 1985, 4, 238-241. ( f ) Rogers, R. D.; Atwood, J. L. Organometallics 1984,3,271-274. (g) Means, C. M.; Means, N. C.; Bott, S. G.; Atwood, J. L. J.Am. Chem. SOC.1984,106,7627-7628. (4) Howell, J. M.; S a p , A. M.; Singman, E.; Snyder, G. J.Am. Chem. SOC. 1982,104,4759-4759. (5) Bozik,J. E.; Beach, D. L; Harrison, J. 3. J. Organomet. Chem. 1979, 179, 367-376 and references cited therein. (6)Tucci, E. R. Ind. Eng. Chem. Prod. Res. Deu. 1966,5, 161-165. (7) (a) Harrison, J. J.; Montagna, J. C. Sep. Sci. Technol. 1982, 17, 1151-1163. (b) Atwood, J. L. Recent Deu. Sep. Sci. 1977, 3, 195. (c) Atwood, J. L. In Inclusion Compounds;Atwood, Davies, MacNicol, Eds.; Academic Press: London, 1984; Vol. I.
0276-7333/87/2306-0343$01.50/0
Scheme I NaCAl2EteFl
NaCAIEt3Fl k- 1
+
AlEt3
Scheme I1
r
Et
1
L
perature, we observed by ‘HNMR the characteristic averaging of ethyl resonances, indicative of rapid exchange when A1,Et6 was mixed with M[A12Et6X] complexes. Exchange was demonstrated by plotting the ‘H chemical shift of the methyl resonance in mixtures of Al2Ek and Na[Al,Et,$] vs. the mole fraction of Na[A12Et$]. A linear dependence was observed (Figure 1). The exchange process is of interest from a mechanistic point of view. We have considered two possible mechanisms for the exchange process. The first involves dissociation of M[A12E&X] to form M[A1Et3X] plus A1Et3 (Scheme I). The second involves a bimolecular associative mechanism to form an alkyl-bridged complex with fivecoordinate aluminum (Scheme 11). Both mechanisms have precedence in the l i t e r a t ~ r e . ~ A variable-temperature 13C NMR study was carried out by using a mixture of A12Et, (0.23 g) and Na[A12EbF] (0.27 (8) (a) Mole, T.; Jeffrey, E. A. Organoaluminium Compounds; Elsevier: Amsterdam, 1972; p 171. (b)Swift, H. E.; Itzel, J. F., Jr. I m r g . Chem. 1966, 11, 2048-2050. (9) Oliver, J. P. Adu. Organomet. Chem. 1977, 16, 111-130 and references cited therein.
0 1987 American Chemical Society
